Carburetor choke altitude compensation

ABSTRACT

A carburetor has an air passage in a parallel arrangement with the induction passage for supplying supplemental air around the venturi to the air/fuel mixture in response to changes in ambient operating conditions, the air bypass passage being controlled by a first valve sensitive to changes in ambient conditions, the passage including an additional valve connected to the choke valve for restricting additional airflow in proportion to closing of the carburetor choke valve to provide a desired rich starting and running mixture varying with changes in ambient operating conditions.

United States Patent [191 Freismnth 1 CARBURETOR CHOKE ALTITUDECOENSATTON Inventor: Richard ,1. Freismuth, Mt. Clemens,

Mich.

Assignee: Ford Motor Company, Dearbom,

Mich.

Filed: Nov. 3, 1972 Appl. No.: 303,662

US. Cl 261/39 A, 261/63, 261/46, 48/180 A, 123/119 F,123/124 A Int. Cl.F02m ll/li) Field of Search 48/144, 160, 180 A, 180 C, 48/180 R, 180 M,180 P; 261/63, 39 A, DIG. l, DIG. 2, 46; 123/124 R, 124 A, 119 D, 119 F,120

References Cited UNITED STATES PATENTS 3/1914 Mayer 48/180 A Aug. 27,1974 2,495,299 l/l950 Taner 23/119 3,011,770 .2/1961 Stoltman 1 261/393,721,428 3/1973 Gele et al. 261/23 A Primary ExaminerS. Leon BashoreAssistant ExaminerPeter F. Kratz Attorney, Agent, or FirmKeith L.Zerschling; Robert E. McCollum ABSTRACT 8 Claims, 1 Drawing Figure 4 600'2 Jo 0" O CARBURETOR CHOKE ALTITUDE COMPENSATION This inventionrelates, in general, to a carburetor for an internal combustion engine.More particularly, it re lates to one that compensates for changes indensity of the air due to changes in altitude and/or temperature.

Most production type carburetors in use today have no means forcorrecting the carburetor airflow requirements to compensate for changesin air density as a result of changes in altitude or temperature. As aresult, increases in altitude cause a richening of the mixture andconsequently off-design operation. This is especially noticeable duringcold starting operation when the conventional choke valve is essentiallyclosed. More specifically, as altitude increases, the lower density ofthe air coupled with the lower volume of air as a result of closing ofthe choke valve will result in a richer than normal starting runningmixture.

Carburetor constructions are known in which air bypass passages areprovided to vary the supply of air when ambient operating conditionschange. For example, Stoltman US. Pat. No. 3,011,770, AltitudeCompensated Carburetor, shows such an air bypass passage controlled by abellows to provide additional air as required by the changing ambientoperating conditions. The air bypass passage in this case has an inletconnected to the induction passage between the choke valve and theventuri and an outlet connected to portions both above and below theconventional throttle valve. The outlet connection as described byStoltman permits correction for changing ambient operating conditionsduring engine idle speed operation as well as during other periods. Asthe altitude increases, the lowering density of the air is offset by theincrease of air through the bypass passage.

While the Stoltman device shows compensating means for correcting forchanges in air density, it does not provide additional air for leaningout the starting mixture when the choke valve is closed during coldweather operation. That is, when the choke valve of the Stoltman deviceis closed, the additional air bypass passage also is effectively blockedoff, and, accordingly, the starting mixture will be richer than desired,in the manner stated above.

The invention eliminates the above objection by providing a constructionin which an additional air supply not only is maintained but alsocontrolled during the choking operation as well as at other times sothat the air/fuel mixture is compensated during all engine operationsfor changes in air density or temperature.

It is a primary object of the invention, therefore, to provide acarburetor construction that is sensitive to changes in ambientoperating conditions to compensate for changes in air density to provideessentially a constant calibrated fuel/air ratio for any given speed/-load condition of the engine.

It is another object of the invention to provide a carburetor with anair bypass passage flowing air around the carburetor venturi, thepassage being controlled by first valve means that is responsive toambient temperature and pressure changes to compensate for changes inair density, and an additional control valve connected to the chokevalve to decrease the additional supply of air to the air passage inproportion to the closing of the induction passage when the choke valveis moved towards an engine starting position, to maintain the desiredrich starting mixture.

Other objects, features and advantages of the invention will become moreapparent upon reference to the succeeding detailed description thereof,and to the drawing illustrating the preferred embodiment thereof;wherein, the single FIGURE is a schematic crosssectional view of aportion of a carburetor embodying the invention.

The FIGURE shows a portion 10 of a downdraft type carburetor. Itincludes the usual air induction passage 12 having one end 14 open toair at essentially atmospheric pressure. The opposite end 16 is adaptedto be connected to the intake manifold of an internal combustion engine,not shown, so as to subject the induction passage to the changes inengine vacuum level.

The passage 12 includes the usual choke valve mounted on a shaft 20rotatably mounted in the walls of the air horn section of thecarburetor. The choke valve is variably rotatable by the usualmechanism, not shown, from the closed position shown to a nearlyvertical position permitting unrestricted flow of air through theinduction passage.

Passage 12 also includes a conventional main venturi 21 and a boosterventuri 22. Fuel is inducted, in a known manner, through a tube 24 intobooster venturi 22, where it is mixed with the air from inlet 14 forflow past a throttle valve 26. The latter is mounted on a shaft 28rotatably mounted in the walls of the carburetor body.

Further details of construction and operation of the carburetor per seare not given since they are known and are believed to be unnecessaryfor an understanding of the invention. Suffice it to say that duringnormal cold start operations, the choke valve 18 is in the essentiallyclosed position shown restricting airflow through the carburetor. Thestrong vacuum signal from the engine pistons causes a supply of fuel tobe drawn from the idle system, not shown, and mixed with the smallamount of air available so that the starting mixture is rich. As soon asthe engine is started, the conventional dechoking mechanism will crackopen the choke valve 18 by a slight amount sufficient to permitcontinued operation of the engine at a leaner air/fuel ratio.

In this instance, the carburetor body is formed with an air bypasschamber 29 communicating with a bypass passage 30. An air inlet 32communicates air at ambient or essentially atmospheric pressure level tochamber 29. One discharge 34 of air passage 30 is located below venturi22 so as not to cause a metering of fuel through venturi 22 by the air.Passage 30 has an additional discharge outlet 36 located below theclosed position of throttle valve 26 to provide additional air duringclosed throttle, engine idle speed operation.

Airflow through passage 30 is controlled in this in stance by a valvemeans 38 that is movable in response to ambient operating changes. Morespecifically, the valve means consists of a lower needle valve portion40 adapted to cooperate with a valve seat 42 formed in a portion ofpassage 30. It further includes a conical valve 46 that is biasedagainst a seat 48 by a spring 49 to variably block or open the flow ofair to outlets 34 and 36. Conical valve portion 46 has a finger actuator50 engaging a stern extension of the valve, the actuator being formed onone end of a lever 52. The latter is hinged at 54 and movably engaged byan aneroid or bellows 56.

The bellows 56 defines a sealed interior chamber under atmospheric orsome chosen reference pressure and temperature. A change in the ambientpressure and temperature conditions causes the bellows or aneroid 56 toexert a force upon the connecting lever 52 to move the valve 38 upwardlyor downwardly, as the case may be, to thereby vary the airflow throughbypass passage 30.

Completing the construction, the inlet 32 to chamber 29 is controlled bya secondary choking valve 60 rotatably mounted in the carburetor body.Upstanding ears 62 and 64 project from each of the choke valves 18 and60, and are pivotally interconnected by a link 66 for joint rotation.

In operation, when the ambient operating conditions are the same as thereference used for the interior of bellows 56, then the parts will bepositioned with the additional air passage 30 closed. The carburetorthen will operate in a conventional manner with no additional air beingadded to the air/fuel mixture inducted into the intake manifold portion16. As the ambient temperature increases, or if the altitude rises, thedensity of the air taken into the carburetor will also change. However,since the induction of fuel and air through the carburetor is on avolume basis rather than by weight, there normally would be a change inthe air/fuel ratio with a resultant richening of the mixture. However,with the construction as shown, a rise in temperature level or increasein altitude will cause the bellows 56 to raise the valve 38 against thebias of spring 49 to open the air passage 30 for passage of additionalair to induction passage 12. The additional air will compensate for theloss in density to provide a substantially constant air/fuel ratio forthe particular engine speed and load.

During idle speed operation, throttle valve 26 will be essentiallyclosed. Accordingly, compensation for changes in density at this timewill be made by the addition of air through the outlet 36 instead of 34.

During choking operation, both the choke valves 18 and 60 will be movedtowards an essentially closed position shown. The closed position ofchoke valve 60 controlling the volume of airflow through inlet 32 willof course be such in proportion to ambient operating conditions thatenough additonal air will flow through passage 30 during chokingoperation when ambient conditions so warrent that the starting andrunning choking operations will not be overrich or richer thanconventional choking operation; yet, the control will be such as to notpermit an unlimited supply of air to valve 46, which could make thestarting mixture too lean.

While the invention has been described and shown in its preferredembodiments, it will be clear to those skilled in the arts to which itpertains that many changes and modifications may be made thereto with-'out departing from the scope of the invention.

l claim:

1. A carburetor having an induction passage connected to air at one endand to an engine intake manifold at the opposite end and having aventuri connected to a source of fuel for the induction thereof into thepassage in response to airflow therepast, a choke valve mounted anteriorof the venturi and rotatable at times to control airflow therepast,means defining a separate air passage in a parallel airflow relationshipto the induction passage bypassing the venturi for supplying additionalair to the induction passage at a location below the venturi, ambientpressure and temperature responsive means for controlling the overallair/fuel ratio in the intake manifold by controlling airflow through theair passage to compensate for changes in air density of the air in theinduction passage with changes in altitude and temperature, and controlmeans coupled to the choke valve to maintain a controlled supply of airto the air passage when the choke valve is rotated to a chokingposition.

2. A carburetor as in claim 1, the control means comprising a secondvalve controlling the airflow to the air passage.

3. A carburetor as in claim l, the pressure and temperature responsivemeans including a further valve movable with respect to the air passagein response to ambient operating conditions to control the airflowtherethrough.

4. A carburetor as in claim 3, the control means comprising a secondvalve controlling the inlet of air to the further valve.

5. A carburetor as in claim 2, including linkage means movablyconnecting the choke and second valves to variably control the flowthrough both passages.

6. A carburetor as in claim 1, the ambient pressure and temperatureresponsive means comprising a bellows connected to valve meanscontrolling the flow of air through the air passage and spring biased toclose the air passage.

7. A carburetor having an induction passage connected to air at one endand to an engine intake manifold at the opposite end and having aventuri inbetween connected to a source of fuel for the induction offuel into the passage in response to airflow therepast, a choke valvemounted anterior of the venturi and rotatable at times to controlairflow through the passage, means defining an air passage separate fromthe induction passage for supplying air thereto around the venturi, theair passage having an air inlet in parallel with the induction passageair inlet and connected at its other end to the induction passage belowthe venturi, valve means movable in response to ambient pressure andtemperature changes for controlling airflow through the air passage tocompensate for changes in air density of the air in the inductionpassage with changes in altitude and temperature, and additional valvemeans in the air passage air inlet pivotally connected to the chokevalve for concurrent operation for controlling the supply of air to theair passage when the choke valve is rotated to a choking positionessentially closing the induction passage air inlet and decreasing theadditional air passage airflow in proportion to the choking of the airin the induction passage.

8. A carburetor as in claim 7, the ambient pressure and temperatureresponsive means comprising a be]-

1. A carburetor having an induction passage connected to air at one endand to an engine intake manifold at the opposite end and having aventuri connected to a source of fuel for the induction thereof into thepassage in response to airflow therepast, a choke valve mounted anteriorof the venturi and rotatable at times to control airflow therepast,means defining a separate air passage in a parallel airflow relationshipto the induction passage bypassing the venturi for supplying additionalair to the induction passage at a location below the venturi, ambientpressure and temperature responsive means for controlling the overallair/fuel ratio in the intake manifold by controlling airflow through theair passage to compensate for changes in air density of the air in theinduction passage with changes in altitude and temperature, and controlmeans coupled to the choke valve to maintain a controlled supply of airto the air passage when the choke valve is rotated to a chokingposition.
 2. A carburetor as in claim 1, the control means comprisIng asecond valve controlling the airflow to the air passage.
 3. A carburetoras in claim 1, the pressure and temperature responsive means including afurther valve movable with respect to the air passage in response toambient operating conditions to control the airflow therethrough.
 4. Acarburetor as in claim 3, the control means comprising a second valvecontrolling the inlet of air to the further valve.
 5. A carburetor as inclaim 2, including linkage means movably connecting the choke and secondvalves to variably control the flow through both passages.
 6. Acarburetor as in claim 1, the ambient pressure and temperatureresponsive means comprising a bellows connected to valve meanscontrolling the flow of air through the air passage and spring biased toclose the air passage.
 7. A carburetor having an induction passageconnected to air at one end and to an engine intake manifold at theopposite end and having a venturi inbetween connected to a source offuel for the induction of fuel into the passage in response to airflowtherepast, a choke valve mounted anterior of the venturi and rotatableat times to control airflow through the passage, means defining an airpassage separate from the induction passage for supplying air theretoaround the venturi, the air passage having an air inlet in parallel withthe induction passage air inlet and connected at its other end to theinduction passage below the venturi, valve means movable in response toambient pressure and temperature changes for controlling airflow throughthe air passage to compensate for changes in air density of the air inthe induction passage with changes in altitude and temperature, andadditional valve means in the air passage air inlet pivotally connectedto the choke valve for concurrent operation for controlling the supplyof air to the air passage when the choke valve is rotated to a chokingposition essentially closing the induction passage air inlet anddecreasing the additional air passage airflow in proportion to thechoking of the air in the induction passage.
 8. A carburetor as in claim7, the ambient pressure and temperature responsive means comprising abellows.